A conventional multiphase circuit breaker generates ionized gases within each phase of the circuit breaker during the circuit interrupt condition. Modern circuit breaker designs are more compact and generate additional power in smaller spaces than conventional circuit breakers. Due to the reduction of internal space and higher current levels, the gases produced when opening the circuit in question are more intense and at higher temperatures. When a compact current limiting circuit breaker, such as that described in U.S. Pat. No. 4,963,849 entitled "Compact Current Limiting Circuit Breakers" is used within an industrial power distribution circuit, intense arc gases are generated during overcurrent circuit interruption. These high temperature gases must exit the circuit breaker enclosure in order to prevent the circuit breaker enclosure from becoming over-stressed. Ventilated circuit breakers provide openings within the circuit breaker enclosure to allow the ionized gases to exit the circuit breaker in a controlled manner.
The U.S. patent application Ser. No. 07/736,673, filed Jul. 26, 1991, entitled "Molded Case Circuit Breaker Arc Exhaust Gas Controller" describes one means for controlling the egress of gases from the circuit breaker enclosure. The arc gases exiting through the ventilation slot of one line terminal compartment must be prevented from contacting a line terminal connector within an adjacent line terminal compartment to prevent a so-called "phase-to-phase" fault. The typical approach to prevent the occurrence of short circuits between the line end conductors of different phases is to each conductor with insulating tape. This practice is labor intensive and expensive.
The U.S. patent application Ser. No. 07/836,573, filed Feb. 18, 1992 , entitled "Arc-Proof Molded Case Circuit Breaker" describes one means of decreasing the intensity of the exiting arc exhaust gases so that the connecting busbars need not be separately shielded.
Another means is described in U.S. Pat. No. 4,181,836, wherein the exhaust openings of the circuit breakers are enclosed in a boot and the arc gases exiting the different phases of a circuit breaker remain therein. However, the boot does not provide separation of the gases from the different phases, it merely shields the metal enclosure in which the circuit breaker is mounted from being contacted by the arc gases. The boot merely provides additional space for the gases to expand to relieve the pressure therein.
Thus, the aforementioned solution has limited utility in circuit breakers that have higher interruption circuit levels. These solutions do not afford sufficient protection from the short circuit in higher interruption circuit level circuit breakers, because these types of circuit breakers generate greater amounts of energy and the gases become trapped within the boot without sufficient time to clear.
U.S. patent application Ser. No. 07/611,203 entitled "Bus Cover and Lug Cover for a Molded Case Circuit Breaker" describes a cover utilized in a double-branch configuration of circuit breakers and is a permanent fixture thereupon.
U.S. patent application Ser. No. 872,195 entitled "Circuit Breaker Phase Current Barrier" describes a phase barrier that is disposed at the line end of a circuit breaker to redirect the arc exhaust gases exiting from the circuit breaker. The phase barrier described therein can be utilized with a bus-plug type of system.
One purpose of the present invention is to provide protection from short circuits for higher level interruption circuit breakers during the interrupt condition.
Another purpose of the present invention is to provide protection that can be field installed as an add-on feature to any type of circuit breaker.